12V (AUX 18L) new battery voltage shows 11.9V

[alohart]

That's a great knowledge on the charging mechanism on i3. I'm sure that other i3 owners would be pleased to know that they can skip the overpriced OEM battery with ancient tech to LFP with no problem on charging.

I would caution any i3 owner living in a climate with cold winter weather not to buy a LFP battery that doesn't include an automatic cell heater. The Ohmmu battery that would fit an i3 and would definitely have a cell heater, the LFP battery for a Rivian truck, is considerably more expensive than the OEM battery or the G1DC22-B deep cycle LFP battery that you are considering and that doesn't claim to include an automatic cell heater.

You are right on LFP voltage output curve, it is quite flat throughout the capacity range, so traditional charger should see it as close to full when LFP is at 50% or more in capacity.

My CTEK battery charger that doesn't include a LFP setting isn't confused by the higher voltage of my Ohmmu LFP battery. According to the Ohmmu smartphone app, my charger charges the battery to 100%.

 

[neversummer]

I would caution any i3 owner living in a climate with cold winter weather not to buy a LFP battery that doesn't include an automatic cell heater. The Ohmmu battery that would fit an i3 and would definitely have a cell heater, the LFP battery for a Rivian truck, is considerably more expensive than the OEM battery or the G1DC22-B deep cycle LFP battery that you are considering and that doesn't claim to include an automatic cell heater.

My CTEK battery charger that doesn't include a LFP setting isn't confused by the higher voltage of my Ohmmu LFP battery. According to the Ohmmu smartphone app, my charger charges the battery to 100%.

I just replaced my wife's i3 12v battery this afternoon, and I can see it could tricky to install OEM battery terminal on Ohmmu.

I think I should get Ohmmu's Rivian battery since I don't know where my car will end up if I decide to get a different EV in the future. At least next owner won't have to worry about using the car in cold weather.

Thank you so much!

 

[Dutchi3]

I wonder that if the LFP battery is kept at 100% charge all the time, will it shorten the lifespan of the battery? Or does it have a buffer built in? Maybe LFP is less susceptible of high SoC.

 

[alohart]

I wonder that if the LFP battery is kept at 100% charge all the time, will it shorten the lifespan of the battery? Or does it have a buffer built in? Maybe LFP is less susceptible of high SoC.

I am concerned about that after I noticed that our LFP 12V battery is almost always near a 100% charge level in our i3. I am not aware of any charge level buffers in this LFP battery. Fully charging an LFP battery cell is recommended, but it is not recommended to allow it to remain fully charged for long periods. For its longest life, battery cell experts recommend storing a LFP battery cell at a 50% charge level just like other lithium chemistries.

I will try disabling the charging of our LFP battery until its charge level decreases below 50%. I can disable charging using the Ohmmu smartphone app that communicates with the battery's BMS via Bluetooth. I can also monitor the 12V battery's charge level with the Ohmmu app, so with a little effort, I could probably keep the average charge level near 50%. The voltage at 40% is 13.1V which is higher than the full charge voltage of the OEM battery, so the car wouldn't notice that the 12V battery's charge level is 40%. I would have to learn how fast it discharges while parked so that the 12V battery's charge level doesn't decrease too low.

However, I have a spare LFP battery, so if managing the charge level of the LFP battery is too onerous, I could just ignore its charge level and replace it with my spare LFP battery when it fails.

 

[BattlePenguin]

I just replaced my wife's i3 12v battery this afternoon, and I can see it could tricky to install OEM battery terminal on Ohmmu.

I think I should get Ohmmu's Rivian battery since I don't know where my car will end up if I decide to get a different EV in the future. At least next owner won't have to worry about using the car in cold weather.

Thank you so much!

Did you have to register the battery with the car? I don't have the equipment to do the registration, so I was thinking about asking paying BMW to do it, but they want $300 for the installation. Did you install your battery by yourself and skip registration? If you did not skip registration, what tool did you use to register the batter? Maybe the procedure is called by other names, but the person at BMW told me that you have to do that step in order for the car to take full advantage of the battery or the battery to get full power... something like that

 

[neversummer]

I wonder that if the LFP battery is kept at 100% charge all the time, will it shorten the lifespan of the battery? Or does it have a buffer built in? Maybe LFP is less susceptible of high SoC.

Did you have to register the battery with the car? I don't have the equipment to do the registration, so I was thinking about asking paying BMW to do it, but they want $300 for the installation. Did you install your battery by yourself and skip registration? If you did not skip registration, what tool did you use to register the batter? Maybe the procedure is called by other names, but the person at BMW told me that you have to do that step in order for the car to take full advantage of the battery or the battery to get full power... something like that

I replaced the battery myself, but I bought the battery from local BMW dealer. My local BMW dealer also wanted about $300, $299 to be exact, and claimed that it's that price b/c they have to register the battery. Registration is needed only if you install different size battery, but since I bought OEM, the setting is the same. I did use BimmerCode, you can buy from App store, with Bluetooth ODBC reader to double check original setting to see if it was set at 20AH.

The procedure was straight forward, just pure mechanical labor, nothing to reprogram and not even setting the clock. It will show incorrect time once new battery is installed, but it will automatically sync the time with GPS once your car has clear view of the sky.

 

[alohart]

Registration is needed only if you install different size battery, but since I bought OEM, the setting is the same. I did use BimmerCode, you can buy from App store, with Bluetooth ODBC reader to double check original setting to see if it was set at 20AH.

BimmerCode can change the battery capacity or type from the default OEM 20 Ah AGM battery, but BimmerLink is required to register a replacement battery. Registration records the date and maybe mileage when the battery was replaced so that a mechanic would know in the future when the battery had been replaced.

There's no evidence that registration affects 12V battery charging on an i3 as it does on BMW vehicles with alternators, so I wouldn't pay a mechanic to register a replacement battery. For what a mechanic would charge, one could license BimmerLink and buy an OBD to WiFi or Bluetooth adapter to register the battery oneself.

 

[neversummer]

BimmerCode can change the battery capacity or type from the default OEM 20 Ah AGM battery, but BimmerLink is required to register a replacement battery. Registration records the date and maybe mileage when the battery was replaced so that a mechanic would know in the future when the battery had been replaced.

There's no evidence that registration affects 12V battery charging on an i3 as it does on BMW vehicles with alternators, so I wouldn't pay a mechanic to register a replacement battery. For what a mechanic would charge, one could license BimmerLink and buy an OBD to WiFi or Bluetooth adapter to register the battery oneself.

Thank you for the correction

 

[BattlePenguin]

Ok, I think I'm all set. I'll let you know how it goes.

 

[JoeCool88]

As I've seen on my 2018 94Ah i3, the 12V battery has an of course essential, but on the other hand very limited role to play in the cars electric architecture. This role is to supply enough energy to fullfill the commands from the remote control, e. g. to unlock it when the car is stationed/locked. But as soon as you press the starter button w/o breaking, or start a function like e. g. the pre-heating or pre-AC remotely, the DC-DC converter jumps in and supplies 14 V to the car, thus charging the 12V battery. And even after switching down and closing the i3, the 14 V supply remains active for a few minutes.
Taking into consideration the short period of time and relatively low current when needed, as well as a certain self-discharging when not engaged and the battery's weight, BMW dimensioned it not bad imho.
In aviation industry the policy is to replace some items i. a. w. their mean time between failure (MTBF). If experience shows that, due to the operational constraints and climate conditions, a battery 'dies' after 5-6 years (= MTBF), in aviation they would replace it after 3 years. I would suggest to replace the i3 12V battery systematically after 4 years.
At a price for a standard battery (like the AUX18L20Ah, TX24HL or YTX24HL-BS) of approx. 100 to 150 Euro/USD, this means 25 to 37 Euro per year. The local BMW dealer will charge you that for opening his door. But highly likely you will never ever face any 12V battery issues on your i3.
This might be ancient tech, but keeps the type certificate of the car valid. And might safe you from the one or other uncomfortable question from your insurance, in case of an even small electrical fire on the car, which occured for which reason ever ;o).

 

[mtkkk45]

When I was looking for a LFP battery whose physical size was similar to the OEM battery, I looked through Ohmmu's automotive batteries but not their deep cycle batteries. The batteries for the Rivian truck were the perfect physical size, but I didn't need 2 batteries. I asked Ohmmu about selling me only 1 Rivian battery (at that time, there was no option to buy only 1 as there is now) plus 2 Tesla Model S screw-on brass SAE terminals. Ohmmu told me that they were interested in offering a LFP battery for the i3 but didn't have an i3 to perform a test fitting. They told me that they would sell me a battery for only the shipping cost if I would document the installation in our i3 which I agreed to do.

I was surprised when I received 2 LFP batteries with generic labelling, 2 sets of SAE posts, and 2 ¼" fitting spacers. I discovered that they were ⅜" taller than the OEM battery and ½" taller than the Rivian battery which makes installation more difficult than it would have been for a Rivian battery. Thanks for alerting me of the G1DC22-B whose measurements match those of the batteries I received, so I assume that I have 2 G1DC22-B's rather than Rivian batteries.

The increased LFP battery height meant that I had to move the spacer from the underside of the horizontal section of the battery hold-down bracket to the inside of the vertical section of this bracket so that the top bracket screw would align with its nut. I mounted 1 Ohmmu fitting spacer on the front of the battery with double-sided tape. The relocated spacer plus the Ohmmu spacer allowed the bracket to secure the battery which is ½" less wide than the OEM battery. The shorter length of the LFP battery isn't a problem.

Threading the top bracket screw is still more difficult than with the OEM battery, so I created a thin PET washer from a supermarket strawberry container to secure this screw. I slid this washer onto the top bracket screw from the back side of the bracket which prevents the screw from falling out and disappearing into the void below while trying to thread it into its nut (I was lucky to find this screw when it fell before I made the washer). Because the bracket is higher than with the OEM battery, I added a couple of washers between the bottom of the bracket and the bottom of the battery box.

I initially had problems with the screw-on terminals not making good, solid electrical connections with the battery terminals. Those used with the OEM battery don't fit at all on the LFP battery. The bases of Model S screw-on terminals are too large to fit in the recesses in the battery case around the battery terminals, so I used a Dremel tool to grind a couple of flat areas on the sides of the screw-on terminal bases so that they would fit into these recesses. This has the added benefit of preventing the SAE posts from rotating should their attachment screws loosen.

The undersides of the screw-on terminals are recessed and don't contact the tops of the battery terminals, so I added 2 brass washers to each terminal to fill these gaps and create good, solid electrical connections that don't depend on the stainless steel attachment screws to conduct electricity.

So installing an Ohmmu G1DC22-B battery in an i3 isn't plug-and-play, but it's not too difficult. The Rivian battery would be a better fit but at almost twice the current sale price of the G1DC22-B battery. If you live where ambient temperatures could be cold, the Rivian battery is self-heating so that it would function well in cold weather. There's no such claim for the G1DC22-B battery. This isn't a problem for me in Honolulu, but if you live in a colder climate, ask Ohmmu whether the G1DC22-B battery is self-heating. If not, it might not work well in cold temperatures.

I installed a Ohmmu G1DC22-B battery in our 2019 i3 last November and moved it to our new-to-us 2021 i3 in June. I've had no electrical problems since replacing the OEM battery. The DC-DC converter's 14.0-14.4 output voltage keeps the LFP battery fully charged.

I really like the Ohmmu battery's Bluetooth radio and smartphone app which allow me to monitor the state of the battery (charge level, overall and individual cell voltages, current flow, temperature, cycle count, age, error alerts, and the ability to enable/disable charging and discharging). I could disable discharging so that I wouldn't have to disconnect the battery's negative cable when storing our i3 for several months which I do almost every year. This might also be a security feature that could prevent a thief from starting an i3, but I don't know how an i3 would react to having its 12V power turned off regularly.

I also moved my 12V system logger to our 2021 i3. It shows that the voltage of the Ohmmu battery is typically 0.5V higher than that of the OEM battery and that its voltage doesn't sag nearly as much under load or decrease as much as the battery's charge level decreases. I think that this would prevent many of the diagnostic trouble codes (DTC's) from being stored when the OEM battery fails and its voltage drops too low. Hopefully, the warning signs of the failure of a LFP battery would occur before its output voltage decreases so much that DTC's are stored. I hope that my LFP battery lasts much longer than the typical OEM battery lifetime.

That's a great knowledge on the charging mechanism on i3. I'm sure that other i3 owners would be pleased to know that they can skip the overpriced OEM battery with ancient tech to LFP with no problem on charging. I'll use bimmercode to code the same setting. You are right on LFP voltage output curve, it is quite flat throughout the capacity range, so traditional charger should see it as close to full when LFP is at 50% or more in capacity.

Thank you again for sharing this valuable information and guidance, I'll give it a shot on the installation once arrived. I might have to pm you, so thank you in advance for your help!

Thank you for the correction

Best conversation I’ve heard by far on the 12v AUX.
Live in SoCal near Dodger Stadium …
First, I’ve replaced two 12v myself for both a 2014 i3 and a 2018 i3s and today - 01/14/25 - the i3s battery is dead after replacing oem just 14 months ago - received battery direct from east penn deka in Fontana area from wholesaler. Cost $129.

I’m so intrigued by the Ohmmu G1DC22-B battery need a battery install now but don’t feel confident about this install myself. I’d pay for more advice and assistance… sort of tired of this 12v debacle that has been my only bugaboo since owning two i3’s.

EXTRA NOTE: Found this oem online tonight and seems too good to be true:
$150 free shipping Deka 18L 12v -
https://www.batterywarehouseonline.com/cart.php
.

 

[mtkkk45]

Two notes -
1. For anyone living in Southern California. I’ve replaced two i3 12v batteries myself and sourced oem batteries for cost, But I found a mobile certified mechanic who will replace the battery with the East Penn Deka OEM and register the battery for $350. Tell Harry that Marc sent you. The BMW dealership in Monrovia quoted $500 to install - and that beats other BMW dealerships in LA by $250.

https://h-autorepair.com/

2. If you want a backup OEM AUX 18L Deka / East Penn for by far the cheapest you can find delivered free You can get the OEM for $150 from:
https://www.batterywarehouseonline.com/cart.php